Interpretive Summary: Salmonella typhimurium (St) can cause infection in pigs and can be transmitted to pork, thereby increasing the odds of humans contracting a foodborne illness. We tested the ability of Bifidobacterium lactis (Bb12), a bacterial strain commonly found in dairy products, to eliminate St from a growth chamber in the laboratory. It appears that Bb12 is antagonistic to St. If Bb12 could be fed to pigs and reduce St in pigs, the risk of human infection and foodborne illness by St could also be reduced.

Technical Abstract:
A commercially available probiotic, Bifidobacterium animalis subspecies lactis (Bb12) was adapted to and maintained in a continuous-flow chemostat culture. We evaluated the growth characteristics and interactive effects of Bb12 and a porcine-derived Salmonella typhimurium (St) when cultivated singly or together. When the continuous-flow culture of Bb12 was challenged with 10**4 to 10**7 CFU/ml of St, the St was eliminated within 24 h. This was replicated 4 times. Because the Bb12 chemostatic culture maintained itself at pH 4.5, it appeared that St elimination was due to the reduced pH. Optimum growth of St occurred at ph 5.6 to 5.8. To determine whether the Bb12 effects were due to pH, a second study was designed in which St was grown in pure culture and the pH reduced to 4.5. St concentrations dropped to unculturable levels within 28 h. In a third study, the pH of the Bb12 culture was maintained at pH 5.6 by means of a continuous drip of NaOH and challenged with St. Although at reduced concentrations (10**3 CFU/ml), the St remained in the chemostat until day 9 when the drip was discontinued. Within 24 h, the concentration of Bb12 began to increase and the pH began to decrease. By day 14, the pH was at 4.5 and the St was eliminated. It is apparent in these in vitro studies that Bb12 has antagonistic properties against St and it is possible that there could be some in vivo applications of Bb12 against St.